Many medical patients suffering from any one of a variety of lung ailments are often prescribed supplemental oxygen therapy so that the patient could breath oxygen-enriched air throughout the day and sometimes throughout the night. Earlier supplemental oxygen therapy employed a nasal cannula system operably connected between a tank of compressed oxygen and the patient's nose. Oxygen was continuously delivered to the patient throughout the patient's entire breathing cycle. This method of continuously delivering oxygen to the patient throughout the patient's breathing cycle was considered wasteful because much of the oxygen dissipated into the ambient air environment. Better methods of delivering oxygen to the patient were later developed which included improved equipment that would only deliver oxygen to the patient during the inhalation phase of the patient's breathing cycle. Usually, this improved equipment employed a demand valve which opened to deliver supplemental oxygen to the patient only when the patient inhaled. Numerous types of demand valves are well known in the prior art.
One such demand valve is described in U.S. Pat. No. 5,360,000 to Carter. This demand valve is compact, simplified and totally pneumatic. The demand valve which is coupled between a source of pressurized gas such as oxygen and the patient includes a valve body having a gas flow passageway and pneumatically-coupled sensing and slave diaphragms. The slave diaphragm is interposed in the gas flow passageway and prevents gas from flowing during the exhalation phase of the patient's respiratory cycle. During inhalation, which is sensed by a sensing diaphragm, the slave diaphragm moves to open the gas flow passageway, thus permitting flow of gas to the patient. Although effective in delivering gas to a patient upon demand, this demand valve has an inherent problem. When the patient inhales to cause delivery of oxygen to patient, oxygen is also vented into the ambient air environment for as long as the slave diaphragm remains opened. This leads to wastage of oxygen which is the very problem that demand valves were designed to prevent.
Furthermore, this demand valve has an inherent deficiency of delivering gas to the patient in a continuous flow stream upon and during the inhalation phase. Unfortunately, the air remaining in the patient's respiratory passageway i.e. the nasal cavity and the throat, is first taken into the lungs upon inhalation. The oxygen-enriched air then follows the remaining air and only approximately one-half of the oxygen-enriched air ever reaches the lungs. The remaining one-half of the oxygen-enriched air remains in the patient's respiratory passageway during the waning moments of inhalation and is the first to be exhaled therefrom during exhalation. It would be beneficial to the patient if this air remaining in the patient's respiratory passageway after exhalation could be purged or otherwise enriched with oxygen before it is inhaled. Such an approach is utilized in U.S. Pat. No. 4,686,974 to Sato et al.
There is a need in the industry to provide a pneumatically-operated gas demand apparatus which can control delivery of oxygen to the recipient/patient as the recipient inhales and exhales while minimizing wastage of oxygen. It would be advantageous of this pneumatically-operated gas demand apparatus can deliver a high-flow pulse of oxygen to the recipient/patient upon commencement of the inhalation phase of the patient's breathing cycle. Such a high-flow pulse of oxygen delivered upon commencement of the inhalation phase would enrich the air remaining in the patient's respiratory passageway upon inhalation and, simultaneously therewith, purge some of this air therefrom before being inhaled. It would also be advantageous if this pneumatically-operated gas demand apparatus can deliver a continuous flow of oxygen immediately after delivery of the pulse of high-flow oxygen and throughout the remaining portion of inhalation. The present invention satisfies this need and provides these advantages.